The present invention relates in general to methods of centering a read/write head of a data storage apparatus which stores an information data on a magnetic disk, and in particular to a method of centering such a read/write head on a track of a magnetic disk along which an information data is recorded.
In a data storage apparatus which stores an information data on a magnetic disk along a recording track by means of a read/write head, various methods are proposed for centering the head accurately on the center of the track so that the density of the tracks and thus the recording density on the disk can be increased.
For example, a so-called "Inside Diameter-Outside Diameter Method" or "OD-ID" method is described in NIKKEI ELECTRONICS, July 18, 1983, pp.222-223. According to this method, the innermost and outermost tracks are used as reference tracks, and a minimum stepwise movement of the read/write head performed by a step motor across the magnetic disk is corrected so that the head is positioned exactly on the center of the track of the disk. According to this method, the amount of minute correction to the stepwise movement is obtained for a desired track and the position of the the head is adjusted by applying the correction thus obtained to the minimum stepwise movement of the step motor when the desired track is scanned.
In the aforementioned conventional method, there is a need to keep on watching whether the read/write head is scanning exactly along the center of the track or not in order to secure proper centering of the head. Further, it is necessary to distinguish the two reference tracks. Furthermore, there is a problem in that the magnetic disk may be expanded or contracted particularly in a radial direction when the ambient temperature is changed. Such a deformation of the magnetic disk results in a change in the distance between adjacent tracks which tends to offset the position of the head from the exact center of the track. Such an offset can become a serious problem when the density of the track on the disk is increased. Therefore, in order to secure a reliable operation of the data storage apparatus, there is a need to apply correction to the position of the head so that the position of the read/write head is corrected with respect to such a deformation of the disk. So far, no satisfactory solution to such a problem is known.